Band-Selective, Low-Dispersion Terahertz Attenuators Based on 3D Bulk Metamaterials Leveraging De-latticed Cross-Bar...

Terahertz (THz) optical components for power attenuation and dispersion management require materials that provide isotropic and band-selective control of electromagnetic waves. However, two-dimensional (2D) metasurfaces based on coherent lattice coupling exhibit polarization anisotropy and angular dispersion, which lead to phase distortion. Here, three-dimensional (3D) bulk metamaterials (MMs) functioning as THz attenuators are proposed and experimentally demonstrated based on a de-latticing strategy inspired by amorphous natural materials. Periodic arrays of cross-bar meta-atoms are encapsulated by cyclo-olefin polymer (COP) as randomly oriented cubic meta-grains and dispersed within a COP matrix, forming an amorphous composite that eliminates in-plane coherence. The fabricated samples exhibit band-selective and thickness-tunable attenuation with a smooth refractive-index variation across 0.3-0.4 THz. Compared with the 2D metasurface, the dispersion slope $\Delta n/\Delta f$ decreases from 8.37 to 0.36 at the resonant frequency, indicating an order-of-magnitude suppression of phase dispersion. The attenuation scales continuously with thickness owing to incoherent resonant scattering from randomly oriented dipoles, providing a practical pathway to thickness-dependent and band-selective response. This work demonstrates an isotropic, low-dispersion, and thickness-tunable 3D bulk MMs THz attenuator that overcomes the polarization anisotropy and strong dispersion of conventional 2D attenuators, offering a practical pathway toward integrated THz photonic systems.